You're going to be bombarded with lots of buzzwords in this post - don't be put off. By the end, you'll have a vision of the future of the web you never thought possible. Let's start with Alisa Leonard-Hansen's presentation explaining portable social graphs:
They gives us a glimpse of what the next few years will bring in terms of the whole web becoming social. To quote Charlene Li:
in the future, social networks will be like air. They will be anywhere and everywhere we need and want them to be
We've already implemented Facebook Connect, allowing you to use your Facebook identity to log-on and post comments and for your Facebook friends to get told about those comments in their news feeds (when Gawker Media did this, user registrations were up by 45% and comments up by 16% compared to the previous week).
To really begin to see the potential for yourself, have a look at how The Insider is using it, JC Penney's recent Beware of the Doghouse campaign or the early efforts from Vimeo, Brightkite and Eventbrite.